Efforts to increase H-2 yields from fermentative H-2 production include heat treatment of the inoculum, dissolved gas removal, and varying the organic loading rate. Although heat treatment kills methanogens and selects for spore-forming bacteria, the available evidence indicates H-2 yields are not maximized compared to bromoethanesulfonate, iodopropane, or perchloric acid pre-treatments and spore-forming acetogens are not killed. Operational controls (low pH, short solids retention time) can replace heat treatment. Gas sparging increases H-2 yields compared to un-sparged reactors, but no relationship exists between the sparging rate and H-2 yield. Lower sparging rates may improve the H-2 yield with less energy input and product dilution. The reasons why sparging improves H-2 yields are unknown, but recent measurements of dissolved H-2 concentrations during sparging suggest the assumption of decreased inhibition of the H-2-producing enzymes is unlikely. Significant disagreement exists over the effect of organic loading rate (OLR); some studies show relatively higher OLRs improve H-2 yield while others show the opposite. Discovering the reasons for higher H-2 yields during dissolved gas removal and changes in OLR will help improve H-2 yields.